Introduction to Antibiotics Resistance Antimicrobial resistance (AMR) is resistance of a

microorganism to an antimicrobial drug that was originally effective for treatment of infections caused by it

Penicillin G: first introduced, only 3% of bacteria resistant, now, over 90% are resistant

Many bacterial pathogens are currently resistance to many antibiotics with some organisms are currently resistance to every known antibiotics

WHO’s 2014 report on global surveillance of antimicrobial resistance reveals that antibiotic resistance is no longer a prediction for the future; it is happening right now, across the world, and is putting at risk the ability to treat common infections in the community and hospitals

The Development of a Resistant Strain of Bacteria

Natural & Acquired Resistance1. Natural resistance

Intrinsic resistance: some species naturally insensitive

Chromosomic genetic support

Affect almost all species strains

Existed before antibiotic use (Enterobacter sp. - amoxicillin)

2. Acquired resistance (mutation)

Spontaneous mutation: happen as cells replicate

Gene transfer: usually spread through conjugative transfer of R plasmid

Affects a fraction of strains

Increased with antibiotic use(extended spectrum beta-lactamase producing E. coli)

Mechanisms of Resistance1. Production of enzyme that destroys or deactivates

drug

2. Pump antimicrobial drug out of the cell before it can act

3. Slow or prevent entry of drug into the cell

4. Alter target of drug so it binds less effectively

5. Alter their metabolic chemistry

1. Enzymatic Inactivation Inactivation involves enzymatic breakdown of

antibiotic molecules. A good example is β-lactamase:

Secreted into the bacterial periplasmic space Attacks the antibiotic as it approaches its target There are more than 190 forms of β-lactamase E.g of lactamase activity in E.coli and S. aureus(Extended spectrum beta-lactamases - ESBL)

2. Efflux Pumping Efflux pumping is an active transport mechanism. It

requires ATP

Efflux pumps are found in:

The bacterial plasma membrane

The outer layer of gram-negative organisms

Pumping keeps the concentration of antibiotic below levels that would destroy the cell

Genes that code for efflux pumps are located on plasmids and transposons

3. Decrease Permeability Some bacteria reduce the permeability of their

membranes as a way of keeping antibiotics out

They turn off production of porin and other membrane channel proteins

Seen in resistance to streptomycin, tetracycline, and sulfa drugs

4. Modification of Antibiotics Targets Bacteria can modify the antibiotic’s target to escape its

activity Bacteria must change structure of the target but the

modified target must still be able to function. This can be achieved in two ways: Mutation of the gene coding for the target protein Importing a gene that codes for a modified target

Bacteria have penicillin- binding- protein (PBPs) in

their plasma membranes. These proteins are targets for

penicillin

MRSA (methicillin- resistant - S. aureus) has acquired a gene (mecA) that codes for a different PBP It has a different three-dimensional structure MRSA less sensitive to penicillins

MRSA is resistant to all β-lactam antibiotics, cephalosporins, and carbapenems

Streptococcus pneumoniae also modifies PBP It can make as many as five different types of PBP It does this by rearranging, or shuffling, the genes

Bacterial ribosomes are a primary target for antibiotics. Different antibiotics affect them in different ways. Resistance can be the result of modification of ribosomal RNA so it is no longer sensitive

5. Alteration of Pathway Some drugs competitively inhibit metabolic pathways. Bacteria can overcome this method by using an

alternative pathway Some sulfonamide-resistant bacteria do not

require para-aminobenzoic acid (PABA), an important precursor for the synthesis of folic acid and nucleic acids in bacteria inhibited by sulfonamides, instead, like mammalian cells, they turn to using preformed folic acid

Contributing Factors to Resistance Misuse and overuse of antibiotics

Modern live: travelers carry resistant bacteria

There are more large cities in the world today.

Large numbers of people in relatively small areas

Passing antibiotic-resistant pathogens is easier.

Many large urban populations have poor sanitation

Food is also a source of infection that could affect the development of resistance.

An important social change is the increase in the number of people who are immunocompromised.

Emerging and re-emerging diseases are another source for resistance.

Hospitals are ideal reservoirs for the acquisition of resistance.

Destruction of normal flora allows pathogenic pathogens to dominate

Destruction of normal flora allows pathogenic pathogens to dominate

Impact of Antibiotics Resistance Infections caused by resistance organisms result in

prolonged illness, disability or death

Antimicrobial resistance reduces the effectiveness of treatment; thus patients remain infectious for a longer time, increasing the risk of spreading resistant microorganisms to others

AMR increases the costs of health care

AMR jeopardizes health care gains to society

AMR has the potential to threaten health security, and damage trade and economies

Slowing the emergence and spread of antimicrobial resistance

1. Responsibilities of Physicians: must work to identify microbe and prescribe suitable antimicrobials, must educate patients

2. Responsibilities of Patients: need to carefully follow instructions

3. Educate Public: must understand appropriateness and limitations of antibiotics ; antibiotics not effective against viruses

4. Global Impacts: organism that is resistant can quickly travel to another country, in some countries antibiotics available on non-prescription basis

Approaches to Antibiotic Therapy To Prevent Resistance

Use antimicrobials only when necessary

Maintain high concentration of drug in patient for sufficient time

Use antimicrobial agents in combination

Develop new variations of existing drugs

Second-generation drugs

Third-generation drugs

Search for new antibiotics, semi-synthetics, and synthetics

Design drugs complementary to the shape of microbial proteins to inhibit them

Determination of Drug Efficacy Drug efficacy determined based on clinical and

laboratory parameters

Drug efficacy can be measured by susceptibility testing

Including:

1. Kirby-Bauer Method (diffusion test)

2. Broth dilution test

3. The E test

4. Automatic (Vitek, Vitek 2)

Kirby-Bauer Method for Determining Drug Susceptibility1. Bacteria spread on surface of agar plate

2. 12 disks, each with different antimicrobial drug, placed on agar plate

3. Incubated- drugs diffuse outward and kill susceptible bacteria

4. Zone of inhibition around each disk

5. Compare size of different antibiotics

Dilution Test32 ug/ml 16 ug/ml 8 ug/ml 4 ug/ml 2 ug/ml 1 ug/ml

Sub-culture to agar mediumMIC = 8 ug/ml

MBC = 16 ug/ml

An E test combines aspects of Kirby-Bauer and MIC tests

Thank you….